Rebamipide exhibits anti-inflammatory and anti-ulcer effects in gastrointestinal tract and now has been used as a pharmaceutical. In addition, rebamipide has an increasing action of goblet cell density in cornea and conjunctiva of eyes, which increases the yield of mucin that is an ingredient of mucus and the secretion of mucus and lacrimal fluid, and hereby the cornea and conjunctiva can be protected or stabilized. Therefore, rebamipide is known to be effective in preventing and treating the eye disease caused by dryness of cornea which is appellatively referred as dry eye (JP-A-9-301866).
However, rebamipide does not have a sufficient and long-term-stable solubility in the physiologically neutral pH range where the irritant and dysfunctional demerit for eyes or mucosal tissue is low, and hence it is impossible to prepare a rebamipide-formulation as a water solution, because rebamipide is an acidic compound. Alternatively, it is possible to prepare a water-solution of rebamipide using a surfactant such as an ionic surfactant and a non-ionic surfactant, or a solubilizer such as a cyclodextrin derivative. When administering the formulation, however, such surfactant or such solubilizer might have a biological ingredient in the mucosa dissolved in the solution and might interfere with the activity of rebamipide, which is an action of stabilizing and protecting the mucosa.
On the contrary, using an aqueous pharmaceutical suspension containing a dispersed rebamipide, the above-mentioned demerit as to the low solubility of rebamipide will be overcome and hence it will be possible to prepare a rebamipide-formulation. However, rebamipide usually exists in a powder-form prepared by agglutinating a needle crystal of rebamipide (primary particle, mean particle size: short gage length 0.1-0.5 μm, long gage length 0.2-4 μm) to form a secondary particle thereof (mean particle size: about 10-50 μm), and therefore it is thought to be hard to prepare a suspension of rebamipide from a fine particle of rebamipide. Under the prior art, therefore, in order to equally disperse as a fine particle the agglutinated rebamipide that is a secondary particle, it had been indispensable to add a cellulose derivative that is a water-soluble polymer known as a suspending agent, a surfactant and so on to the mixture containing rebamipide, and further to strongly stir the mixture using a special dispersing/suspending device such as a high pressure homogenizer, a colloid mill, a turbine-type stirring device, a high-speed rotary shear stirring device, and an ultrasonicator.
Furthermore, even if it is possible to disperse rebamipide as a fine particle in an aqueous solution, there are some problems in the prior art, namely, the fine particle of rebamipide will be re-agglutinated as the reserve time passes to re-form the secondary particle or to enlarge the crystalline particle, and the precipitated suspension-particle is not easily re-dispersed as a fine particle.
Under such a background of the prior art, it has been desired to develop an aqueous pharmaceutical suspension containing rebamipide so that rebamipide can be stably dispersed as a fine particle using a simple method and the fine particle cannot be re-agglutinated